Use of Mechanical and Metallurgical Analysis to Evaluate Cause of Fractures in a Cast 310 Stainless Steel Pintle Chain

A pintle chain composed of a cast 310 stainless steel material experienced embrittlement, deformation, and multiple fractures after operating six months inside a furnace. The design is such that the chain travels the length of the furnace, experiencing temperatures cycling between ambient and 1,700 F in an oxidizing atmosphere. Pins comprising the individual chain links had experienced deformation, and in some cases, had also fractured in a brittle manner. The links comprising the chain had also experienced numerous fractures in a brittle manner. An analysis of the loads experienced by the pins and links determined that both the short-term yield strength and the long-term creep strength of the pins had been exceeded at the normal operating temperature of the furnace. Furthermore, metallurgical analysis of the pins and links determined that carburization had taken place, embrittling the pins and links. A change to the original design of the furnace had resulted in the unintended presence of the carburizing atmosphere inside the furnace during the first 6 months of operation. The carburizing atmosphere was alleviated by returning to the original furnace design. Upgrading the alloy selection for the chain provided further resistance to service-related embrittlement, increased ductility when cycling to ambient temperature, and increased high temperature strength. Increasing the size of the links and pins was recommended (an upgrade to a higher chain load rating), but was not practical, given the dimensional constraints of running the chain in the furnace.